A new study shows how dust storms have contributed to Delhi’s worsening air pollution

Dust storms of May 2018, in northern India, have contributed to the deteriorating air quality in the region and the capital city of Delhi, with implications for human health, a study has found. The high death toll from the severe dust storms that lashed across the region a year ago was mainly attributed to the intense winds, which surprised even scientists and meteorologists. But apart from the immediate damage to life and property, drastic changes in air quality from the dust engulfing the region affected far more people with potential implications for human health, stated a team of researchers who analysed the impact of the spell of dust storms that struck the region that month. They reported increases in particulate matter, mainly in Delhi and urge for an early warning system.

Dust storms commonly occur in the Indo-Gangetic Plains – the fertile plains in northern India that stretch all the way to the east – from March to May, the pre-monsoon season. Westerly winds typically bring loose sand and soil particles, picked up from the Arabian Peninsula or the Thar Desert in northwestern India, to the Indo-Gangetic Plains. The dust tends to worsen air quality over the Indo-Gangetic Plains, home to around 900 million people, which can have far-reaching effects on human health. While dust storms are a regular feature in the region, the May 2018 dust storms specifically had a death toll of about 100 people, with around 200 people injured.

“We are concerned that the dust impacts the health of people who get exposed,” said Ramesh P Singh, senior author of the study and professor at Chapman University in the United States. However, he also observed that scattered rains occurring soon after the dust storms tend to clean up the dust, improving air quality.

Lead author Sudipta Sarkar, chief research scientist at NASA’s Goddard Space Flight Center, said the study “highlights and summarises the manifold hazardous effect of dust storms on northern and western India”. During October-November, densely populated cities like Delhi and Kanpur in the Indo-Gangetic Plains are vulnerable to wind-borne long-range air pollution from crop residue burning in the north, and now this study “shows the effect of dust storms during the March-May time frame,” Sarkar pointed out. “This really puts the Indo-Gangetic valley in a unique spot in terms of it being targeted by these different hazardous conditions which are mostly outsourced from other areas.”

Sarkar and Singh along with co-authors Akansha Chauhan and Rajesh Kumar of Sharda University in Greater Noida in Delhi’s National Capital Region gathered data from satellites and ground stations to analyse the changes in various meteorological parameters, aerosol properties and air quality during the three almost back-to-back dust storms that swept northern India in May 2018 – the first of which occurred on May 2 and May 3, the second on May 7-8, and the third on May 12-13.

Worsening air quality in Delhi

For changes in air quality, the team looked at the concentrations of inhalable particles of two sizes: PM2.5, fine particulate matter with a diameter of 2.5 micrometers or below, and PM10, coarser particles with a diameter of 10 micrometers or smaller.

A particle with a diameter of 2.5 micrometers is about 30 times smaller than the diameter of an average human hair. PM2.5 data was obtained from the Central Pollution Control Board for stations located in Delhi (including one set up by the US Embassy), Jaipur and Agra whereas for PM10, the data was available only for Delhi and Jaipur. Delhi experienced the worst air quality compared to the other cities, with both PM2.5 and PM10 concentrations surging notably during the second and third dust storms. This is because of the track of winds carrying the dust, said Singh. “Sometimes the track goes above Delhi, sometimes it goes below Delhi – it all depends on the track of dust.”

Sarkar agreed, adding that in this case and for most dust storms that sweep across northern India during the pre-monsoon season, “Delhi is smack in the middle of the dust-laden winds originating from the Arabian Peninsula or the Thar Desert” and so “no matter if the winds go slightly over or below Delhi, Delhi is most likely to be impacted”.

But why didn’t particulate matter rise substantially over Delhi during the first dust storm, which was also the most deadly? Sarkar explained that during the first storm, “Delhi also had a significant southeasterly wind component from the Bay of Bengal areas. This brought in relatively clear air from that area and as a result, the impact of the dust-bearing wind over Delhi, during this time, was significantly diluted.”

As for Jaipur, it was difficult to detect any significant fluctuations in particulate matter, noted Sarkar, because the city “is subjected to continuous dust-laden winds from the Thar during these months as Jaipur is directly in line with the Thar.”

“Depending upon the nature of the dust storm and its origin, particulate matter changes,” said Gufran Beig, senior scientist at the Indian Institute of Tropical Meteorology in Pune, who was not associated with the study. “In most cases, coarser particles (PM10) increase significantly but in some cases, levels of both finer (PM2.5) and coarser particles enhance.”

An early warning system

In light of the findings and considering that dust storms occur regularly during the pre-monsoon season, the authors call for an early warning system to be implemented so that people stay indoors during the most harmful phases of the storm.

“India must start providing alerts to the public and there should be a website where people can visualise or monitor dust,” said Singh. “We need more air quality stations to study the mixing of anthropogenic [human-generated] emissions and dust along the dust track to study the chemistry of mixing and impacts of dust,” he added.

Beig, who is also the project director of India’s first air quality forecasting system, SAFAR (­System of Air Quality and Weather Forecasting And Research), developed by the Indian Institute of Tropical Meteorology along with partner institutions, the India Meteorological Department and the National Centre for Medium Range Weather Forecasting, said that the system has developed a “new dust scheme” and is now able to provide air quality forecasts from dust triggered by long-range storms from the Gulf region and short-range storms from Rajasthan’s desert up to three days in advance.

SAFAR also has a multilingual mobile app called SAFAR-Air, added Beig. “We keep providing timely information in our website on the daily bulletin,” he said, adding that they also forecast the share of dust/smoke generated from stubble burning.

This article first appeared on Mongabay.